Usually, if you want an ability to separate ingest and processing and allow for extended buffering while also guaranteeing that data is moved off the source host ASAP.

NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB